A circle with circumference $4\pi$ has an arc with a $60^\circ$ central angle. What is the length of the arc? ${4\pi}$ ${60^\circ}$ $\color{#DF0030}{\dfrac{2}{3}\pi}$
Solution: The ratio between the arc's central angle $\theta$ and $360^\circ$ is equal to the ratio between the arc length $s$ and the circle's circumference $c$ $\dfrac{\theta}{360^\circ} = \dfrac{s}{c}$ $\dfrac{60^\circ}{360^\circ} = \dfrac{s}{4\pi}$ $\dfrac{1}{6} = \dfrac{s}{4\pi}$ $\dfrac{1}{6} \times 4\pi = s$ $\dfrac{2}{3}\pi = s$